The invention relates to a method of producing individually formed protheses or implants and in particular, to an endoprothesis including an anchoring pin produced by the method of the invention.
Anchoring of protheses, and particularly of endoprotheses in a human bone has been a major problem in the prior art. This problem occurred with total protheses (for example, hip- head-neck-resection) and for joint-surface-substitute endoprotheses (for example, hip-, head-cap-knee slots-endoprotheses) and also for combinations of protheses (for example, upper shank part of the knee total endoprothesis).
The protheses which substitute for natural body parts vary in sizes, shapes, structures, angular positions, lengths, widths as compared to a relatively small number of filling protheses or endoprotheses, support or volume substituting parts of various materials. This means that a surgeon is in many instances, forced to adjust the bone of a patient to a prothesis model for anchoring the prothesis in the bone. In many cases this means that a bone substance should be removed for adjusting or fitting in the filling prothesis; under both conditions pressure, pulling and torsion forces which can occur on the prothesis insert or on the attachment place must be considered in the bone structure to be adjusted.
With conventional shaft-like implanted endoprotheses (for example hip endoprotheses) a relatively thin prothesis part must be anchored in a wide bone cavity. If there is spongiosa in the bone its balk or mesh structure is disturbed and its initial supporting function can not be carried out.
With conventional cement anchoring endoprotheses spongiosa is totally removed from the bone and a remaining free space formed between the prothesis and compacta of the bone is filled with special fillers, for example bone cement. In this process used for conventional total protheses and for upper surface substituting endoprotheses and the combination of those depending on implantation technique, the thickness of the cement layer, elasticity coefficient and implantation time have been found inefficient (see, for example "Bony Ingrowth Fixation of Aeetabular Components for Canine Toal Hip Replacement" by Harris, W. H., 27 Ann. Meeting Orth. Res. Sec. Vol. 6, page 74).
Tests and research have been conducted for ways of cement-free implantation possibilities which would suggest large volume prothesis shafts, longer prothesis shafts and better shaft-prothesis designs with smaller or thinner cement layers to be utilized.
This research, however, has practically failed because it is merely not possible to determine automatically when the prothesis with adjustable parts is to be used taking into consideration a real number of different lengths, widths of human joints and joint parts with use of filling and preliminarily prepared protheses.
The major problem with conventional techniques is also that eventually the endoprotheses become loosened after being inserted in place and must be readjusted. This happens with joints for total and joint surface substituting protheses and their combinations. With the upper surface substituting prothesis, important force receiving and force distributing bone structures (hard bone bark corticals) or bone mesh (spongiosa) must be removed, for example in cortical compact bone shaft tube for force receiving and force distribution and existing incongruities must be compensated by a filling material.